Rail vehicles, such as locomotives and rail cars, typically have 4-6 axles and each axle is supported by two iron wheels. With continuous operation, wheels undergo considerable mechanical stress and metal fatigue. These stresses may lead to a gradual flattening or cracking of portions of the wheel tread which can create deformities in the wheels. These deformities, such as, but not limited to ‘wheel flats’ or cracked wheels, may damage rails as a rail vehicle passes over the rails. Moreover, if the wheels flatten to a point where they become too wide, then the rail vehicle may become derailed while in operation.
Traditional inspection techniques used in the railroad industry, such as drive-by inspections where all of the wheels on the rail vehicle are glanced at while an inspection vehicle drives by, are not as accurate and reliable as more rigorous and quantitative inspection methods. Many damaged wheels aren't found, while many useable wheels are removed when they could remain in service.
The financial impact of a rail vehicle becoming out of service is significant since it can mean a service disruption. Furthermore, by the time a flat wheel may be manually or visually detected, a convenient opportunity to service the flat wheel may have passed and the rail vehicle may have to wait for service and thus the rail vehicle may be taken out of service thus causing a service disruption. Wheel deformities may be detected by direct inspection and measurement of rim thickness or by determining that the deformation on the wheel surface will lead to a part of the wheel not touching the tracks. This loss of contact may be detected using either electrical or optical signals. However, these methods also do not provide adequate notice of wheel deformities to avoid service disruptions. If risky wheels can be detected ahead of time and service crews alerted, then service disruptions may be averted.